1. Field of the Invention
The present invention relates to a separation membrane to be utilized, beginning with gas-separation, in a wide variety of separation such as microfiltration, ultrafiltration, reverse osmotic separation and the like, and a process for manufacturing the same.
2. Related Art Statement
In a field of gas-separation, etc. where a specific gas is separated from a mixed gas by a gas-diffusion there have been employed separation membranes having micropores with an average pore size of between several tens of .ANG. and several hundreds of .ANG. which is much smaller than the mean free paths of gas molecules. Although organic high polymer membranes, as conventional separation membranes of this kind, have been generally used, they are not employable for temperatures higher than 100.degree. C. and, moreover, are inferior in corrosion resistance and durability, so that various problems still remain in their practical uses.
Further, aiming an improvement of heat resistance, there are known processes for producing porous separation membranes by sintering metallic powders and/or ceramic powders. Separation membranes according to such a process are, however, difficult to form into 1 mm thick or less, due to a question of strength and, therefore, have have a lack of practicability yet, as a separation membrane of gas-separation which is desired to improve its separation efficiency, with decreasing thickness to the possible utmost extent.
An attempt was made, as described in the Gazette of Japanese Patent Application Laid-open No. 59-59,223, to obtain a permeable membrane consisting of a multi-layered porous body, by impregnating a porous body, such as a ceramic sintered body, with a solution of a permeable membrane-forming component, such as aluminum alcoholate, aluminum chelate or the like, hydrolyzing and thereafter drying followed by firing. According to this method, water or an organic binder in the solution is, when transpires, apt to leave cracks and/or foams behind in the permeable membrane, therefore even if the pore size of micropores in the membrane is controlled in the range between several tens of .ANG. and several hundreds of .ANG., a major part of gas will eventually diffuse through perforations having a pore size of several tens of microns formed by cracks, so that the resulting membrane has such a shortcoming that desired gas-separation is hardly effected.